Implantable medical devices are used to treat patients suffering from a variety of conditions. Examples of implantable medical devices include implantable pacemakers and implantable cardioverter-defibrillators (ICDs), which are electronic medical devices that monitor the electrical activity of the heart and provide electrical stimulation to one or more of the heart chambers as necessary. Pacemakers deliver relatively low-voltage pacing pulses in one or more heart chambers. ICDs can deliver high-voltage cardioversion and defibrillation shocks in addition to low-voltage pacing pulses
Pacemakers and ICDs generally include pulse generating circuitry required for delivering pacing and/or cardioversion and defibrillation pulses, control circuitry, telemetry circuitry, and other circuitry that require an energy source, e.g. at least one battery. In addition to a battery, ICDs include at least one high-voltage capacitor for use in generating high-voltage cardioversion and defibrillation pulses. Implantable medical devices (IMDs), including pacemakers, ICDs, drug pumps, neurostimulators, physiological monitors such as hemodynamic monitors or ECG monitors, typically require at least one battery to power the various components and circuitry used for performing the device functions.
IMDs are preferably designed with a minimal size and mass to minimize patient discomfort and prevent tissue erosion at the implant site. Batteries and capacitors, referred to collectively herein as “electrochemical cells,” contribute substantially to the overall size and mass of an IMD. Electrochemical cells used in IMDs are provided with a hermetically-sealed encasement for housing an electrode assembly, including an anode and cathode separated by a separator material, a liquid electrolyte, and other components such as electrode connector feed-throughs and lead wires. The encasement includes a case and a cover that are sealed after assembling the cell components within the case.
An access port, often referred to as a “fill port”, provides an opening through the encasement for filling the cell with a liquid electrolyte after sealing the cover to the case. Fill ports typically include a fill tube extending through the encasement, often through a sidewall of the case, surrounded by a ferrule welded to the sidewall to support the fill port components. After filling the encasement with a liquid electrolyte, the fill port is welded closed to form a hermetic seal. The fill port is typically welded closed using a filler member or material, such as a ball, button or cap, placed in the lumen of the fill port tube. The filler separates the electrolyte liquid and other internal cell components from the weld joint. Examples of fill ports including a filler member or material are generally described in U.S. Pat. No. 6,157,531 (Breyen et al.), U.S. Pat. No. 6,844,106 (Heller et al.) and U.S. Pat. Application Publication No. 2004/0064163 (Aamodt et al.). The encasement wall is generally made thick enough to support the fill port components and to withstand swelling that occurs as the cell discharges.
As it is desirable to minimize overall IMD size, electrochemical cell designs, including access port designs that allow cell size and mass to be reduced are desirable. Reduction of electrochemical cell size may allow balanced addition of volume to other IMD components, thereby increasing device longevity and/or increasing device functionality. Other electrochemical cell design considerations motivating new cell designs include reducing manufacturing cost and time.